This invention relates generally to inflatable restraint systems and, more particularly, to an apparatus and method for inflating an inflatable device such as an inflatable vehicle occupant restraint for use in such systems.
Many types of inflator devices have been disclosed in the art for inflating an air bag for use in an inflatable restraint system. One type of inflator device involves the utilization of a quantity of stored compressed gas which is selectively released to inflate the air bag. To properly inflate a typical air bag at an appropriate rate, such a type of device commonly requires the storage of a relatively large volume of gas at relatively high pressures. As a result of the high pressures, the walls of the gas storage chamber are typically relatively thick for increased strength. The combination large volume and thick walls results in relatively heavy and bulky inflator designs. In addition, a technique designed to initiate the release of the stored gas into the air bag must be devised.
Another type of inflator device derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the air bag. Typically, such gas generating materials can produce various undesirable combustion products, including various solid particulate materials. The removal of such solid particulate material, such as by the incorporation of a filtering device within or about the inflator, undesirably increases inflator design and processing complexity and can increase the costs associated therewith.
In addition, the temperature of the gaseous emission of such inflator devices can typically vary between about 500.degree. F. (260.degree. C.) and 1200.degree. F. (649.degree. C.), dependent upon numerous interrelated factors including the desired level of inflator performance, as well as the type and amount of gas generant used therein, for example. Consequently, air bags used in conjunction with such inflator devices typically are constructed of or coated with a material resistant to such high temperatures. For example, an air bag such as constructed of nylon fabric, in order to resist burn through as a result of exposure to such high temperatures, can be prepared such that the nylon fabric air bag material is coated with neoprene or one or more neoprene coated nylon patches are placed at the locations of the air bag at which the hot gas initially impinges. As will be appreciated, such specially fabricated or prepared air bags typically are more costly to manufacture and produce.
Further, while vehicular inflatable restraint systems are preferably designed to be properly operational over a broad range of conditions, the performance of such inflator device designs can be particularly sensitive to changes in the ambient conditions, especially temperature. For example, operation at very low temperatures, such as temperatures of -40.degree. F. (-40.degree. C.), can affect the performance of various propellants, and thus lower air bag pressure resulting from an inflator which contains a fixed available amount of propellant.
In a third type of inflator device, air bag inflating gas results from a combination of stored compressed gas and combustion of a gas generating material. This type of inflator device is commonly referred to as an augmented gas or hybrid inflator. Hybrid inflators that have been proposed heretofore are subject to certain disadvantages. For example, inflator devices of such design typically result in a gas having a relatively high particulate content.
Various specific inflator devices and assemblies have been proposed in the prior art. U.S. Pat. No. 5,263,740 discloses an assembly wherein within a single chamber is housed both an inflation gas and a first ignitable material, which is subsequently ignited therein.
The housing of both an inflation gas and an ignitable material within a single chamber can result in production and storage difficulties. For example, concentration gradients of such components, both initially and over time as the device awaits actuation, can increase the potential for the release therefrom of ignitable material into the air bag prior to complete ignition, as well as increasing the relative amount of incomplete products of combustion released into the air bag.
Also, gas generators wherein, for example, a fuel and an oxidant are stored in a single chamber, can under certain extreme circumstances be subject to autoignition (i.e., self-ignition) and the consequent dangers that may be associated therewith, both during manufacture and storage.
Further, as the gas mixture resulting from such a single storage chamber assembly will typically be at a relatively high temperature, such designs can be subject to the same or similar shortcomings identified above associated with high temperature emissions.
In addition, as a result of the rapid pressure and temperature rises normally associated with inflator devices which house a mixture of oxidant and ignitable material, proper and desired control and operation of such inflator devices can be difficult and/or complicated.
Thus, there is a need and a demand for improvement in air bag inflators to the end of overcoming the foregoing disadvantages. More particularly, there is a need for the provision of air bag inflation gas at a relatively low temperature and having a relatively low concentration of undesirable combustion products, especially particulate matter. Further, there is a need for an inflator device of simple design and construction which device is effectively operable using a variety of fuels, oxidants, and stored gases. In addition, there is a need for an inflator design that reduces or eliminates the potential of autoignition of an inflation gas/ignitable material mixture. Still further, there is a need for the provision of air bag inflation gas containing no more than limited amounts of oxygen gas and moisture, thereby avoiding or minimizing the problems associated therewith. Yet still further, there is a need for an inflation device that minimizes or avoids the introduction of combustible mixtures into the air bag upon inflation.
In addition, there is a need for an inflator assembly design that safely provides greater design and manufacturing flexibility.
The present invention was devised to fill the gap that has existed in the art in certain of these respects.